JP6016835B2 - Radiation detection - Google Patents

Description

The present invention relates to an instrument and method for measuring neutron radiation, in particular for measuring the neutron dose equivalent rate.

Accurate measurement of the neutron dose rate can be done by accurately examining the environment in which work involving personnel access is intended and / or the radiation dose to personnel working in environments where significant radiation is present. It is important to ensure that it is well below acceptable limits. It is also important to ensure that the dose rate in the public access area is below acceptable limits.

In most cases, the neutron field consists of neutrons with a wide range of energies. The spread of the energy distribution and the proportion of dose in each energy range are important because they vary in the level of biohazard. Accordingly, there is a need in the art for an apparatus that can accurately detect neutrons having low energy (<0.4 eV), intermediate energy (0.4 eV to 10 eV), and high energy (10 keV to 20 MeV).

Prior art instruments have a limited range of neutron energy that can be accurately measured. Particularly in the high energy range, problems arise. This is because there is a high possibility that high energy particles will pass through the device without being detected. This problem is illustrated by the device described in US Pat. No. 4,588,898. In more detail, the use of polyethylene contributes to the slowing down of fast and intermediate energy neutrons, but the amount of polyethylene needed to efficiently slow down high energy neutrons is practical in terms of weight and size. Is difficult. Conversely, the use of excessive polyethylene prevents efficient detection of thermal neutrons (ie, low energy neutrons). Therefore, such an apparatus has low neutron detection efficiency in a part of the energy range.

One means of addressing the above problem is to employ a device that detects neutrons in a limited energy range and apply a “weighting formula” to the results obtained with such a device, resulting in a “total dose equivalent” (Total dose equivalent) ". However, this weighting calculation is often inaccurate because it does not directly measure neutrons over a wide range of energy levels.

A second problem associated with prior art devices is that the sensitivity can vary significantly depending on the energy range to be measured. Thus, if the device in question is calibrated using high energy neutrons, the measurements may be erroneous in the presence of lower energy neutrons. Similarly, if a measurement adjustment can be made using a low energy source, then the measurement of higher energy neutrons will be inaccurate. Although supplementary spectroscopic measurements can be used to determine the energy distribution of the detected neutrons and to apply correction factors, they are time consuming, costly and impractical. Such measurement methods also rely on the neutron field used by the instrument not changing from or within the location.

Previously, the above inaccuracies were accepted. The worst error was thought to be in the less important neutron energy range or when only a small dose equivalent was exposed. Recently, however, it has been found that the relative risk factor for neutrons is greater than previously observed (the maximum quality factor for neutrons has increased from 20 to 30 relative to the maximum quality factor for photons). . As a result, there is a need to improve sensitivity with less error over a wide energy range.

Further complicating the problem is the periodic review of definitions used in radiation protection. This review changes the relative importance of different neutron energy ranges as the neutron quality factor or radiation weighting factor is changed. In view of the nature of many prior art devices, this change requires the device to be reconfigured on a large scale, necessitating hardware replacement or otherwise tolerating large errors. Therefore, a more versatile device is required.

EP 0943106 describes a neutron detector which is improved in several respects from previous detectors. More specifically, the described apparatus is based on a centrally located ³ He nuclear detector, which is installed as a neutron detector in a shallow area below the surface of a decelerating polyethylene sphere 6 Operates in combination with two photodiodes. The centrally located detector is located inside a polyethylene shell encased by a boron compound rubber shell (Flex / Boron). On the outside of the boron compound rubber is a polyethylene shell. In use, the outer polyethylene shell decelerates fast neutrons, the boron compound layer attenuates low energy neutron incidence on the device, and the inner polyethylene shell further decelerates neutrons penetrating the boron compound layer. The device of EP0943106 is able to limit the H ^* (10) response to less than twice the pre-calibrated calibration, which is the existing neutron area inspection instrument (Bartlett et al, 1997). It is a point that has been improved.

The device of EP0943106 offers several advantages in the energy dependence of the response, while requiring seven detectors, it is expensive to build compared to conventional designs. In addition, the need for both high and low voltage power supplies makes such equipment more complex and more expensive. A further problem with the device of EP 0 944 106 is that such a device is relatively heavy, which is particularly problematic when used as a portable device. This is because when using a portable device, it is necessary for the worker to hold the device with his arms fully extended in order to avoid interference by the worker's body.

Therefore, there is a need for a more practical neutron inspection instrument that addresses one or more of the above problems.

U.S. Pat. No. 4,588,898 European Patent No. 0943106

Bartlett, D T, Tanner R J and Jones D G (1997) .A new design of neutron dose equivalent survey instrument.Radat Prot Dosim, 74 (4), 267-271.

The present invention solves one or more of the above problems.

In a first aspect of the invention, an apparatus for radiation detection is provided, such apparatus i) an inner core comprising a neutron detector, ii) an outer core comprising an neutron moderator and having an outer surface, and iii A) includes at least one elongated thermal neutron guide located at the outer core and having an inner end and an outer end; (a) the thermal neutron guide extends from the outer surface of the outer core toward the neutron detector and is used Sometimes, thermal neutrons are guided to the neutron detector, and (b) the inner end of the thermal neutron guide is close to the neutron detector.

In one form, such an instrument, more specifically, an inner core neutron detector, is primarily sensitive to thermal (low energy) neutrons and does not require multiple detectors. In the present invention, low energy (ie thermal) neutrons mean neutrons having an energy of less than 0.4 eV. The thermal neutrons preferably have an average energy (at room temperature) of less than 100 meV, or less than 50 meV, or less than 30 meV, for example in the 25.3 meV region.

In use, such equipment reduces the overestimation of intermediate energy neutrons (0.4 eV to 100 keV), which is characteristic of inspection equipment that has only one other detector.

At the time of work, it is preferable to hold the device away from the worker by the distance of full arm extension. To facilitate this, the maximum weight of the device must be less than 10 kg, for example less than 8 kg or less than 6 kg.

In one form, the neutron moderator is a solid material that includes one or more hydrogen-containing materials, such as one or more plastic materials, such as polyethylene or other hydrogen-containing or hydrocarbon polymers. It is a solid substance. The use of materials having an average density of 0.6 to 1.5 g / cm ³ is preferred, more preferably 0.7 to 1.2 g / cm ³ , still more preferably 0.8 to 1.15 g / cm ³ , Most preferred is 0.90 to 1.00 g / cm ³ .

The neutron moderator may include one or more different materials. In one form, one or more of the different materials may be arranged in layers corresponding to the perimeter of the inner core, preferably in separate layers. In other forms, two or more such different materials may form a composite, mixture, and / or amalgam, arranged as one or more layers, preferably as separate layers, around the inner core. Also good. The one or more different materials preferably have a high thermal neutron capture cross section. In one form, each layer has a thickness from the inner core toward the outer surface of the outer core. By way of example, such a direction is a direction that provides the shortest distance from the inner core to the outer surface of the outer core. In this regard, in one form in which the outer core is substantially spherical, such direction would be substantially radial.

Such an outer core may include neutron attenuating materials such as boron or boron containing materials, cadmium or cadmium containing materials, lithium or lithium containing materials, or composites, mixtures, and / or amalgams thereof. When the neutron attenuating material includes boron or a boron-containing material, the boron may be natural or enriched with a boron isotope such as boron-10. When the neutron attenuating material includes lithium or a lithium-containing material, the lithium may be natural or enriched with a lithium isotope such as lithium-6. The neutron attenuating material may be provided in powder form, provided as a metal layer, or provided in a matrix such as a plastic matrix. In one form, the neutron attenuating material forms one or more layers (preferably separate layers) within the outer core. In one form, the neutron attenuating material may form a layer that defines the inner surface of the outer core. Alternatively, the neutron attenuating material may be sandwiched between neutron moderators located in the outer core, and the sandwiched neutron moderator may be present as a layer.

Preferably, the outer core substantially surrounds the inner core. The outer core may be in contact with the inner core.

The outer core may comprise a carrying handle and / or electronic processing means mounted on the outside. The outer core may have a protruding leg. Alternatively, such processing means may be installed remotely from the apparatus. In use, such processing means communicates with the device. Suitable processing means include one or more of wire connections, optical communications, wireless communications, or other means.

The inner core may include one or two or more neutron detectors, or may include one or more neutron detectors. Such detectors include one or more of: ³ He type; BF ₃ type; and ⁶ Li and ⁷ Li converter pairs, scintillators and photomultiplier tubes, or materials from which delayed beta decay such as silver can be detected. Can be selected. Preferably, such an instrument includes a single neutron sensitive detector or consists of a single neutron sensitive detector.

In one form, the inner core is spherical. Preferably, the thickness of the material surrounding the inner core is substantially equalized by shaping the outer core or matching the dimensions. The outer core may be spherical. Alternatively, the outer core may have a cylindrical shape having a hemispherical tip. In this case, the inner core has a shape corresponding to the outer core, but preferably has a smaller shape.

Such an apparatus may include one or more thermal neutron guides. Such an apparatus preferably comprises at least two or four, or at least six or eight, or at least ten or twelve thermal neutron guides. In one form, such an apparatus includes 14 thermal neutron guides.

The thermal neutron guide is preferably arranged symmetrically around the inner core. In one form, the guide extends generally radially from the inner core or detector toward the outer surface of the outer core.

The thermal neutron guide may extend over the entire length from the outer surface of the outer core to the inner core / detector. Alternatively, the thermal neutron guide may end before the inner core and / or before the outer surface of the outer core. In a preferred form, the thermal neutron guide contacts the inner core, preferably in contact with the centrally located detector.

In one form, the thermal neutron guide is structurally distinct from (and preferably does not include) neutron moderator and / or neutron attenuator.

In one form, the thermal neutron guide extends from the outer surface of the outer core toward the inner core / detector. Such a thermal neutron guide preferably provides a single line-of-sight for directing thermal neutrons from the outside of the device to the inner core. In one form, such a guide is elongated and straight. The thermal neutron guide preferably extends in a direction that provides the shortest distance from the inner core to the outer surface of the outer core. By way of example, in a form in which the outer core is substantially spherical, such direction would be substantially radial.

The thermal neutron guide may contain a solid substance or may be made of a solid substance, preferably a metal such as aluminum or lead, and most preferably aluminum.

Alternatively, the thermal neutron guide may comprise a fluid material or consist of a fluid material, which is preferably air. In this form, such a guide is preferably provided by drilling in the neutron moderator and / or neutron attenuator. Alternatively, the thermal neutron guide may consist of a vacuum or an incomplete vacuum.

The cross-sectional area of the thermal neutron guide may be substantially constant throughout the length of the guide. Alternatively, the cross-sectional area of the thermal neutron guide may vary throughout the guide length. In one form, such cross-sectional area increases as one moves away from the inner core and approaches the outer surface of the outer core. In a preferred form, the cross-sectional area of the portion of the guide located near the outer surface of the outer core may be larger than the cross-sectional area of the portion of the guide located near the inner core.

In one form, the thermal neutron guide extends toward the inner core and the inner end of the guide is close to the detector. For example, the guide inner end may end at a position where the distance between the guide inner end and the internal detector is less than 20 mm, less than 15 mm, less than 10 mm, less than 8 mm, or less than 5 mm. Alternatively, such a guide may extend over the entire length up to the detector located at the center of the instrument (ie, in contact with the detector). In this regard, if there is a significant amount of moderator between the inner end of the guide and the detector, the instrument response will be adversely affected: such a guide will produce an effective response to thermal neutrons. It will not be possible. This problem has been observed in several devices in the prior art, such as the detector described in DE 19627264 C1, and is addressed and solved by the present invention.

The elongate thermal neutron guide may terminate at or near a flat or substantially flat outer end (at or near the outer core outer surface). Alternatively, the outer end may have a concave shaft (eg, as shown in the accompanying figures), such as a sharply concave shape on the inside, a semispherical shape on the inside, a semicircle, a V shape, or a U shape. It may end in a directional cross section. In this way, the guide outer end may be formed to correct the direction dependence of the response for low energy neutrons. For example, if it has a flat guide tip (or a guide tip that is coplanar with the outer surface of the instrument), such an instrument typically responds selectively to neutrons whose incidence plane is parallel to the axis of the particular guide. To do. Instead, it is preferable to provide a concave external guide tip to correct the direction dependence of the response of the device, which is preferred. For example, the concave tip of the guide may have an average concave radius of approximately or a maximum of 20 mm, 15 mm, or 10 mm. The concave feature of the guide is a feature that goes beyond the simple neutron path. This is because the instrument is designed so that it does not respond excessively to neutron incidence from a particular direction. For example, the device may include 2, 4, 6, or 8 such concave guides. With respect to the non-concave guide of the device (eg, a conventional guide), the geographical location / position of the concave guide may be arbitrary. Alternatively, the concave guides may be installed in “pairs”, and the two members of each pair are each positioned to be substantially opposite the detector (eg, each tip of the pair of concave guides). May be opposed to both diametric poles). In one form, the guides of the device are all concave guides.

The guide may include a protective tip to prevent debris from entering the device from the outside environment. The protective tip may be in the form of a plug. By way of example, the plug may be formed from the same material as the moderator or a material selected to assist thermal neutrons entering the thermal neutron guide, such as a metal. In one form, the protective tip material itself does not substantially slow or attenuate neutrons, especially low energy neutrons. Alternatively, the protected tip may be an extension of the material of the outer core material.

In one form, such an instrument can efficiently detect neutrons in the energy range of 0.1 meV to 20 MeV (or more), or in the energy range of 0.5 meV to 15 MeV, or in the energy range of 1 meV to 10 MeV. It is.

In a preferred form, such an instrument can detect neutrons in a substantially non-directional manner. In one form where the device electronics are separated, the response does not vary with angle of incidence. In another form in which the electronic device is associated with the moderator, the response hardly changes with the incident angle on a plane perpendicular to the axis passing through the electronic device and the moderator. In such a form, when 0 ° is defined as the incidence from the opposite side of the electronic device in the axis passing through the electronic device and the moderator, the response hardly changes at an arc angle of ± 150 ° from the axis.

In a second aspect of the present invention, there is provided a radiation detection method using the apparatus of the first aspect of the present invention. Such methods include contacting the instrument with neutrons, generating one or more signals following contact of the neutron and neutron detector, and detecting the one or more signals.

In a further aspect of the invention, a method is provided for improving the detection of thermal neutron incidence in an instrument comprising a neutron detector. Such a method includes selectively directing thermal neutrons along at least one elongated thermal neutron guide having an inner end ending proximate to the detector and subsequently detecting it with a neutron detector. .

A further aspect of the invention provides for the use of an elongated thermal neutron guide in a thermal neutron detection instrument. Such a guide ends at a position close to the detector and, in use, such a thermal neutron guide directs the thermal neutrons towards the neutron detector. Such a thermal neutron guide is a feature located inside the moderator / absorber,
・ Effectively induce neutrons at the center of the device
・ Adjust the induction efficiency according to the direction and energy of the neutron,
• Designed to ensure a path through the absorber layer to the centrally located detector.

Such a guide may vary in cross-sectional area so that the instrument does not selectively detect neutrons within a specific energy range.

Various aspects of the invention are described with reference to the following drawings.

It is a figure which shows sectional drawing of one form of the apparatus of this invention. A thermal neutron guide is shown extending from the inner core (detector) to the outer surface of the outer core. The outer core includes a neutron attenuation layer sandwiched between neutron moderation layers. FIG. 5 shows the fluence response for aluminum, copper, and lead rods of 1.5 cm cross-sectional diameter extending from the internal detector to the outer surface of the device. The data is for a boron-compounded polyethylene damping layer with an inner radius of 3.7 cm and an outer radius of 4.9 cm. FIG. 9 shows H ^* (10) response data for rods with cross-sectional diameters of 15 mm and 6 mm extending to the moderator outer surface. FIG. 2 is a longitudinal cross-sectional view of an apparatus in one form of the present invention showing a neutron guide, an inner core, and an outer core polyethylene moderator and polyethylene damping material. FIG. 5 shows fluence response data for an aluminum rod that reaches the outer core outer surface of the device or ends at 5 mm directly below the outer surface. Such data relates to an aluminum rod with a diameter of 6 mm. FIG. 6 shows H ^* (10) response data for an aluminum rod that reaches the outer core outer surface of the device or ends at 5 mm just below the outer surface. It is a figure which shows the effect by changing arrangement | positioning of a neutron attenuation | strengthening boron mixing layer regarding the aluminum guide of 6 mm in cross-sectional diameter extended from the detector located in the center to the place just under 5 mm of the outer core outer surface of an apparatus. Guide cross-sectional diameter, and is a diagram illustrating the effect of varying both the thickness of CH ₂ located between the thickness of CH ₂ covering the guide tip, i.e. the guide tip and the external surface of the outer core. FIG. 6 shows the H ^* (10) response of an example design, showing data from optimization calculations and data for more energy. Three energy distributions were also used: thermal energy distribution, ²⁵² Cf source distribution, and ²⁴¹ Am-Be source distribution. These are not displayed as part of the curve. It is a figure which shows H ^* (10) response with respect to a unidirectional source and an isotropic source. The unidirectional radiation source is oriented in the direction along the axis of the two guides. These data relate to a neutron guide with a flat outer end. FIG. 6 shows the H ^* (10) response of a device with a neutron guide that penetrates the neutron absorbing layer but does not extend further until it reaches the detector. Also shown as a control is the H ^* (10) response of a device with a guide that guides the entire neutron to the centered detector. It is determined that perforations that do not extend over the entire length up to the centrally located detector cannot efficiently induce thermal and low energy neutrons for detection. FIG. 6 shows the ambient dose equivalent response characteristics of the device of the present invention in comparison with the peripheral dose equivalent response characteristics of the device by Leake and the device of European Patent No. 094106; It is a figure which shows the apparatus which put the hemispherical insertion part in each guide front-end | tip part in order to correct the direction dependence of the response in low energy. The plug at the guide tip may be made of the same material as the external moderator or a material selected to facilitate assembly or modify response characteristics. It is a figure which shows the surrounding dose equivalent response characteristic of the apparatus which put the hemispherical insertion part of radius 7mm in the guide front-end | tip part. This device was made for a parallel plane neutron field and an isotropic neutron field. This result must be contrasted with the result shown in FIG. FIG. 2 shows a cylindrical device with a single neutron guide. FIG. 2 shows a “bullet type” device, which has two neutron guides in the form of a straight line passing through the center of the device. Additional guides project on this side of the page and on the other side, for a total of four guides. FIG. 3 shows a cubic device with four neutron guides in a plane passing through the center. Additional guides protrude on this and other sides of the page, making a total of six guides. FIG. 3 shows a cubic device with a complex pattern of guides. Such guides include a guide that extends from the outside to the damping layer, a guide that extends from the center of the device to the damping layer, and a guide that penetrates the damping layer.

In the apparatus, six thermal neutron guides are arranged orthogonally around the inner core (four are shown in the figure) (see FIG. 1). Neutron-moderating layer of the outer core comprises a polymeric material in which the CH ₂ of polyethylene-based. The neutron attenuation layer of the outer core includes a boron-containing material such as boron-blended polyethylene.

The inner core includes a neutron proportional counter. When a neutron is incident on such a counter tube, alpha particles are generated through a ¹⁰ B (n, α) reaction in BF ₃ or protons and tritons are generated through a ³ He (n, p) T reaction. , Ionization can occur. A pulse is detected, producing a signal that is sent from the detector to the electronics. Thus, the detector provides a signal that indicates the number of events in the detector. The signal from the detector can be monitored and recorded for a considerable period of time.

Test parameters The form shown in FIG. 1 was investigated. Such an apparatus has the following characteristics.

The centrally located detector used in this design has the dimensions of a Centronic SP9 spherical proportional counter using ³ He as the fill gas.

The apparatus described in Example 1 was prepared with various different types of neutron guides. When assembled, such a guide has a cross-sectional diameter of about 1.5 cm and extends to the outer surface of the outer core. Three very different metals, copper, aluminum and lead, were selected for investigation. These metals were selected for the following reasons.
Copper: has an intermediate density and a relatively high (n, 2n) reaction cross section (˜0.6b), which provides a high ability to enhance the response to high energy neutrons.
Aluminum: Lightweight, very permeable to thermal neutrons, and has a low (n, 2n) reaction cross section (˜0.035b).
Lead: very permeable to thermal neutrons and has a high (n, 2n) cross section (~ 2b).

For neutron energies above 1 MeV, the choice of metal is not important (Figures 2 and 3): Using lead increases the response in the range above 20 MeV compared to aluminum or copper, Only about 20%. At lower energies (eg, thermal neutrons), the response when using a lead rod is 34 times higher than the response when using a copper rod, and the response when using an aluminum rod is when using a copper rod. The response is 250 times higher. The main reason for this sensitivity is that the (n, γ) reaction cross sections are significantly different. Considering the density, the capture cross sections of lead and copper are 4 times and 66 times the capture cross sections of aluminum, respectively. Thus, any of these metals can be employed as a neutron guide for the purposes of the present invention, but it is preferred to use aluminum because of its high permeability to thermal neutrons. Alternatively, other metals that can be easily machined may be used if they have a low atomic mass and do not have a strong neutron capture reaction cross section.

When using lead or aluminum in a 1.5 cm diameter guide, the H ^* (10) response to thermal and intermediate energy neutrons is high (FIG. 3). The difference between the lead and aluminum data may be related to the stronger elastic scattering of lead: probably because more neutrons scatter out of the guide. This difference is not related to the radiation capture cross section for thermal neutrons. This is because the radiation capture cross section is 0.231b for aluminum and 0.174b for lead. For fast neutrons, the (n, γ) reaction cross section of lead is much higher than that of aluminum and has many resonances, but for such energy range, neutrons decelerated in the CH ₂ layer The response must be determined.

For aluminum and lead, the response to thermal neutrons clearly indicates that these rods are efficient in obtaining thermal and intermediate energy neutrons through boron-blended polyethylene. Aluminum is also low in density, so it can save much weight.

The device described and used in Example 2 includes a neutron guide that extends to the outer core outer surface of the device. In this example, an apparatus in which the thermal neutron guide does not reach the outer surface of the outer core is described and used. In this embodiment, a guide having 5 mm of polyethylene is used between the guide tip and the outer surface of the outer core (FIG. 4).

The result of this new arrangement is contrasted with the result of the guide reaching the surface of the device in FIGS. These data indicate that for all energies above 10 keV, no difference in response occurs in the calculations. This is because such energy neutrons are not slowed down or attenuated much in the first 5 mm on the outer surface side of the outer core.

The H ^* (10) response (FIG. 7) is significantly improved by this improvement, and the thermal neutron response is only slightly lower after the improvement compared to the fast neutron response.

This example shows how the fast neutron response of the device of the invention can be modified by the position of the neutron attenuating layer, here the boron-blended polyethylene layer.

In each case, the thickness of the boron-blended polyethylene layer was not changed and remained at 1.2 mm. Three different arrangements of neutron attenuation layers were investigated: inner and outer radii 32mm and 44mm; 37mm and 49mm; 42mm and 54mm. These increments of 5 mm do not produce a particularly significant effect on the response for energies of 10 eV or less, and simply show that the response to neutrons with such energy is determined by neutrons moving along the guide ( FIG. 7). For higher energies, the response increases as the attenuation layer is moved away from the center of the device. This is because the effect of the attenuation layer is reduced and deceleration by the inner core becomes more effective.

Regarding the apparatus described in Example 3, two locations were changed at the same time to obtain the apparatus described in this example. In the first place, the cross-sectional diameter of the guide was reduced from 6 mm to 5 mm. In the second place, the tip of the guide was extended by 1 mm and ended at 4 mm instead of 5 mm from the outer surface of the outer core of the apparatus. Because it is these changes that are complementary is intended, two places were simultaneously subjected to changes: that reducing a guide diameter, but would reduce the thermal neutron response, reducing the CH ₂ covering the guide tip Would increase the thermal neutron response.

The effect of these changes is not dramatic. No change was detected in the response for neutron incidence having an energy of 10 keV or higher (FIG. 8), indicating that the response to such energy is not highly dependent on the guide. There is also no significant difference with respect to thermal neutrons, which will probably show that narrowing the guide offsets the reduction in polyethylene that must be traversed to reach the guide. Thermal neutrons are the least penetrating neutrons and therefore it will be at the guide ends that they will most strongly penetrate the guide.

For neutrons with energies between 0.1 eV and 5 keV, such two simultaneous changes result in a reduced response. In the calculated data, the most notable difference is at 10 eV, and these changes result in a nearly 40% decrease in response. At 5 keV, the response improves and reduces the degree of potential overestimation at such energy.

As more source energy is used, the energy dependence of the response is seen in more detail (FIG. 9). At this time, it can be seen that the H ^* (10) response minimum value is when the energy is about 20 eV and 200 keV, and the response maximum value is when the response is 5 keV.

Three energy distributions were also used as radiation sources: 300K Maxwell-Boltzmann distribution (thermal energy distribution), and ²⁵² Cf and ²⁴¹ Am-Be radionuclide sources (ISO, 2001). The lines shown do not link these sources because they are only intended to match single energy response data. It can be seen that the response to thermal neutron energy distribution is higher than the response expected from single energy data. A value of 11.4 pSv cm ² was used as a conversion factor from fluence to dose equivalent to calculate the thermal neutron ambient dose equivalent response. This is a value applicable only to a single energy neutron field of 10.6 pSv cm ² at 25.3 meV, compiled by ICRU (International Commission on Radiation Units and Measurements) and ICRP (International Commission on Radiological Protection). Is different. The calculated response in such an energy distribution is significantly higher than the response of a single energy neutron field. For fast neutrons, the response to an isotropic source in MCNP is confirmed to be the same as the response to a unidirectional source (FIG. 10).

Preferred embodiments of the invention are characterized by having the specifications shown in Table 2. This design will have a total moderator mass of 4.52 kg.

On the premise that adding electronics and batteries would only add 1 kg to the total mass, such devices would be significantly lighter than other commercial designs: NMS017 (Leake) has a mass of 6.2 kg SWENDI-II is 13.4 kg; Wedholm Medical 2222D is 10.5 kg; Berthold LB6411 is 9.0 kg. Devices of less than 6 kg are relatively easy to use on the job site, so the design of this example would be attractive only with this feature.

Users will not only be attracted by the lightness of the test equipment of the present invention, but will also be interested in the performance of dosimetry: obtain very light weight without acceptable dose equivalent response characteristics There are many possible devices. For example, NMS017 uses a 5 inch diameter reduction sphere (radius 6.35 cm), so the total mass is only 2 kg, but the H ^* (10) response to fast neutrons is 3 orders of magnitude lower than the response to thermal neutrons . Since the H ^* (10) response for the region of the keV energy range of such equipment is an order of magnitude higher than the response for thermal neutrons, the response varies more than 1000 times in the energy range up to 20 MeV.

Of the widely used neutron inspection instruments, the most directly worthy of comparison is the one designed by Leake because it is the lightest. Especially at high energies, dosimetry performance is not as good as some other instruments, but it is most widely used in the UK. Compared to the device of the present invention (FIG. 11), it can be seen that overestimating the numerical value in the keV energy range is substantially reduced in the device of the present invention. The lack of response to thermal neutrons is resolved, and the fast neutron response is slightly better. Compared with the Leake device, the energy dependence of the response characteristics is clearly superior.

The product with the best response characteristics in the prior art is probably a product of the design of NRPB (British Radiation Protection Agency) / BNFL (British Nuclear Fuel Company, now BNG) with seven detectors and a device mass of about 10 kg (Bartlett et al, 1997) (FIG. 11). However, the response characteristics of the NRPB / BNFL device are generally inferior compared with the device of the present invention. In particular, the drop in response at 100 keV and the peak at 5-10 MeV are reduced or eliminated using the guides of the present invention. These latter two characteristics are very important at the work site. Such NRPB / BNFL devices were also substantially heavy and would have caused significant operational inconvenience.

Preferred forms of the invention have the specifications shown in Table 3. This design will have a moderator with a total mass of about 5 kg. Such a design differs from Example 6 in that the guide is filled with air / vacuum instead of aluminum and the radius of the guide changes at a position passing through the damping layer. The function of such a guide is simply to induce thermal neutronized neutrons, so that the guide is thinner in the part through the inner moderation layer, whereas in the part through the outer moderation layer, the guide is a thermal neutron Functions to guide and selectively accept. Since the boron-containing attenuation layer in this embodiment is located further away from the detector, it assists the response to high-energy neutrons. The boron-containing damping material in Example 6 is preferred for a neutron field that does not contain the important elements of fluence from high-energy neutrons.

A preferred form of such a device uses the parameters specified in Table 3 in Example 7, with the addition of a hemispherical insert at each guide tip as shown in FIG. The radius of the outer section of the neutron guide in each case is 0.7 cm and the radius of the sphere forming the insert is 0.7 cm. The center of such a sphere is located 0.75 cm below the outer surface of the speed reducer.

In this embodiment, a boron-containing attenuation layer may be arranged as described in Table 2 or Table 3 in Example 6 or 7, respectively.

Cited references
Bartlett, DT, Tanner RJ and Jones DG (1997) .A new design of neutron dose equivalent survey instrument.Radat Prot Dosim, 74 (4), 267-271.

Briesmeister JF (Ed) (2000). MCNP-a general Monte Carlo n-particle transport code, Version 4C. Report No. LA-13709-M. Los Alamos: LANL.

International Organization for Standardization (2001a) .Reference neutron radiations-Part 1: characteristics and methods of production.ISO 8529-1: 2001 (E). Geneva: ISO.

Leake JW (1965) .A spherical dose equivalent neutron detector.Nucl Instrum Meth, 45, 151-156.

Leake JW (1968). An improved spherical dose equivalent neutron detector. Nucl Instrum Meth, 63, 329-332.

Leake JW (1999). The effect of ICRP (74) on the response of neutron monitors. Nucl Instrum Meth, A421, 365-367.

Tanner, RJ, Molinos, C, Roberts, NJ, Bartlett, DT, Hager, LG, Jones, LN, Taylor, GC and Thomas, DJ (2006) .Practical implications of neutron survey instrument performance.HPA-RPD-016 (Chilton : HPA).

Claims (56)

A device for detecting radiation,
i) an inner core containing a neutron detector;
ii) an outer core having an outer surface; and
iii) contains a metal or fluid and has an inner end and an outer end and is located in the outer core;
Including a plurality of elongated thermal neutron guides,
(a) the thermal neutron guide extends from the outer surface of the outer core toward the neutron detector;
The outer core includes a neutron moderator having a higher neutron moderating ability than the elongated thermal neutron guide, and in use, directs thermal neutrons to the neutron detector;
(b) the heat neutron guide end, proximate to the neutron detector, said plurality of thermal neutron guides, Ri ends with at less than the inner 20mm of the external surface of the outer core,
(c) the outer core is made of a neutron moderator,
machine. The instrument of claim 1, comprising a single neutron detector. The apparatus of Claim 1 or 2 which can detect the neutron of the energy range of 0.1 meV-20 MeV. The apparatus according to claim 1, wherein the neutron moderator of the outer core includes a plastic material having an average density of 0.6 to 1.5 g / cm ³ . The apparatus in any one of Claims 1-4 in which the thermal neutron guide inner edge part and the neutron detector are separated by the maximum distance of less than 20 mm. Thermal neutron guide end and the neutron detector and has spaced at a maximum distance of less than 15 mm, apparatus according to any one of claims 1-5. Outer core further comprises one or more different materials are arranged as a layer in the external core device according to any of claims 1-6. 8. The device of claim 7 , wherein the one or more different materials are neutron attenuating materials. 9. An apparatus according to claim 7 or 8 , wherein the one or more different materials are boron or a boron-containing material. The device according to any one of claims 7 to 9 , wherein one or more different materials are sandwiched between the first and second layers of the neutron moderator layer. Outer core has a thickness of 5Cm～25cm, apparatus according to any one of claims 1-10. Outer core has a thickness of 5Cm～20cm, apparatus according to any one of claims 1-10. Outer core has a thickness of 5Cm～15cm, apparatus according to any one of claims 1-10. The device according to any one of claims 7 to 10 , wherein the one or more layers have a thickness of 0.5 cm to 3 cm. The device according to any one of claims 7 to 10 , wherein one or more layers have a thickness of 0.7 cm to 2 cm. The apparatus according to any one of claims 7 to 10 , wherein the one or more layers have a thickness of 1 cm to 1.5 cm. i) One or more different materials are present as layers and have a thickness of 0.5 cm to 3 cm;
ii) the first neutron moderating layer is disposed near the inner core and has a thickness of 0.5 cm to 5 cm;
iii) the second neutron moderating layer is disposed near the outer surface of the outer core and has a thickness of 5 cm to 20 cm;
The device according to claim 10 . 18. The device of claim 17 , wherein the one or more different materials have a thickness of 0.7 cm to 2 cm. 19. Apparatus according to claim 17 or 18 , wherein the one or more different materials have a thickness of 1 cm to 1.5 cm. The apparatus according to any one of claims 17 to 19 , wherein the first neutron moderating layer has a thickness of 0.7 cm to 4 cm. The apparatus according to any one of claims 17 to 20 , wherein the first neutron moderating layer has a thickness of 1 cm to 3 cm. The apparatus according to any one of claims 17 to 21 , wherein the second neutron moderating layer has a thickness of 5 cm to 15 cm. The apparatus according to any one of claims 17 to 22 , wherein the second neutron moderating layer has a thickness of 7 cm to 12 cm. The device according to any of claims 7 to 16 , wherein one or more different materials surround the inner core. 25. Apparatus according to any of claims 1 to 24 , wherein the neutron attenuating material surrounds the inner core. A plurality of thermal neutron guides free of neutron attenuating material, apparatus according to any one of claims 1 to 25. 27. Apparatus according to any of claims 1 to 26 , wherein the inner core comprises a neutron detector. 28. Apparatus according to any of claims 1 to 27 , wherein at least one thermal neutron guide extends to the inner core. 30. The apparatus of claim 28 , wherein the at least one thermal neutron guide contacts the neutron detector. The apparatus according to any one of claims 1 to 29 , wherein the plurality of thermal neutron guides do not include a neutron moderator. The apparatus according to any one of claims 1 to 30 , wherein the plurality of thermal neutron guides do not include a hydrogen-containing solid substance. The device according to any one of claims 1 to 31 , wherein the plurality of thermal neutron guides do not include a boron-containing material. A plurality of thermal neutron guides, extending radially toward the inner core to the external surface of the outer core, apparatus according to any one of claims 1-32. The apparatus according to any one of claims 1 to 33 , wherein the plurality of thermal neutron guides include or consist of a solid. 35. The apparatus of claim 34 , wherein the plurality of thermal neutron guides comprises or consists of a metal. 36. The apparatus of claim 35 , wherein the plurality of thermal neutron guides comprises or consists of a metal selected from the group comprising aluminum, copper, and lead. The apparatus according to any one of claims 1 to 33 , wherein the plurality of thermal neutron guides includes a fluid. 38. The apparatus of claim 37 , wherein the plurality of thermal neutron guides comprises air, vacuum, or incomplete vacuum, or consists of air, vacuum, or incomplete vacuum. The apparatus according to any one of claims 1 to 38 , wherein a transverse (radial direction) cross-sectional area of each of the plurality of thermal neutron guides is the same throughout the entire length of the guide. The apparatus according to any one of claims 1 to 38 , wherein a transverse (radial direction) cross-sectional area of each of the plurality of thermal neutron guides is not the same throughout the entire length of the guide. Regard transverse (radial) cross-sectional area of the plurality of thermal neutron guides each cross-sectional area of the guide portion located near the external surface of the outer core is larger than the cross-sectional area of the guide portion located near the inner core, according to claim 40 Equipment described in. 42. Apparatus according to any of claims 1 to 41 , wherein the plurality of thermal neutron guides terminates less than 10 mm inside the outer surface of the outer core. 43. Apparatus according to any of claims 1 to 42 , wherein the plurality of thermal neutron guides terminate at a concave tip. 44. The apparatus of claim 43 , wherein the plurality of thermal neutron guides terminate in a concave tip having an average concave radius of up to 15 mm. The apparatus according to any one of claims 1 to 44 , wherein a plurality of thermal neutron guides include a protective tip for preventing debris from entering the guide. 46. The apparatus of claim 45 , wherein the protective tip includes a plug, is an extension of a plurality of thermal neutron guide walls, or is an extension of an outer core. 47. Apparatus according to claim 45 or 46 , wherein the protective tip comprises a neutron moderator or a material that is permeable to thermal neutrons. 48. The device of claim 47 , wherein the protective tip comprises polyethylene. 49. Apparatus according to any of claims 1 to 48 , comprising at least six neutron guides. 50. Apparatus according to any of claims 1 to 49 , comprising at least 10 neutron guides. 51. Apparatus according to any of claims 1 to 50 , wherein the thermal neutron guide is arranged in a symmetrical pattern inside the outer core. The method includes contacting an instrument with neutrons, generating one or more signals subsequent to contacting the neutrons with a neutron detector, and detecting the one or more signals. A method for detecting radiation using the device according to any one of to 51 . 53. The method of claim 52 , wherein the neutron comprises thermal neutrons that are directed toward the neutron detector by a plurality of thermal neutron guides. 54. The method of claim 52 or 53 , wherein the neutron comprises a neutron that is not a thermal neutron. 55. A method according to any of claims 52 to 54 , wherein the thermal neutrons have an average energy of 25.3 meV at room temperature. 56. A method according to any of claims 52 to 55 , wherein the instrument detects high energy neutrons simultaneously.